Protein Synthesis and Central Dogma

Protein Synthesis

Central Dogma

• The process by which genetic information is transferred from DNA to proteins
• Consists of two stages: transcription and translation

Transcription

• The process of creating a complementary RNA copy from a DNA template
• Occurs in the nucleus (eukaryotes) or cytoplasm (prokaryotes)
• Initiated when an RNA polymerase enzyme binds to the DNA template
• Results in the formation of a primary transcript (pre-mRNA)

Processing of Pre-mRNA

• In eukaryotes, the primary transcript undergoes several processing steps:
  • 5' capping: addition of a specialized nucleotide to the 5' end
  • Splicing: removal of introns (non-coding regions) and joining of exons (coding regions)
  • 3' polyadenylation: addition of a poly-A tail to the 3' end

Translation

• The process of building a polypeptide chain from amino acids using the messenger RNA (mRNA) sequence
• Occurs in the ribosomes
• Initiated when an mRNA molecule binds to a ribosome
• Requires two types of RNA: messenger RNA (mRNA) and transfer RNA (tRNA)

The Genetic Code

• The set of rules that maps mRNA sequences to amino acids
• Consists of 64 possible codons (sequences of three nucleotides)
• Each codon specifies one of the 20 amino acids or a stop signal
• Degeneracy: multiple codons can code for the same amino acid

Initiation, Elongation, and Termination

• Initiation: the ribosome binds to the mRNA and the first amino acid is brought into place
• Elongation: amino acids are added to the growing polypeptide chain
• Termination: the polypeptide chain is released when a stop codon is reached

Post-Translational Modifications

• Chemical modifications made to the polypeptide chain after translation
• Examples:
  • Folding: the polypeptide chain assumes its native conformation
  • Hydrolysis: the removal of a peptide bond
  • Phosphorylation: the addition of a phosphate group
  • Glycosylation: the addition of a carbohydrate molecule

Protein Synthesis

Central Dogma

• Genomic information is transferred from DNA to proteins through transcription and translation
• These two stages enable cells to express genetic traits

Transcription

• RNA polymerase enzyme binds to DNA template, initiating transcription
• Complementary RNA copy is created from DNA template
• Primary transcript (pre-mRNA) is formed in the nucleus (eukaryotes) or cytoplasm (prokaryotes)

Processing of Pre-mRNA

• In eukaryotes, pre-mRNA undergoes:
  • 5' capping: specialized nucleotide added to 5' end
  • Splicing: introns removed, exons joined
  • 3' polyadenylation: poly-A tail added to 3' end

Translation

• Ribosomes build polypeptide chains from amino acids using mRNA sequence
• mRNA binds to ribosome, initiating translation
• mRNA and tRNA are required for translation

The Genetic Code

• Set of rules mapping mRNA sequences to amino acids
• 64 possible codons (sequences of three nucleotides)
• Codons specify one of 20 amino acids or a stop signal
• Degeneracy: multiple codons code for the same amino acid

Initiation, Elongation, and Termination

• Initiation: ribosome binds to mRNA, first amino acid is placed
• Elongation: amino acids are added to the growing polypeptide chain
• Termination: polypeptide chain is released when a stop codon is reached

Post-Translational Modifications

• Chemical modifications made to the polypeptide chain after translation
• Examples:
  • Folding: polypeptide chain assumes native conformation
  • Hydrolysis: removal of a peptide bond
  • Phosphorylation: addition of a phosphate group
  • Glycosylation: addition of a carbohydrate molecule